Polymer and solar cell using the same

ABSTRACT

A polymer of an embodiment includes a repeating unit containing a bivalent group represented by the following formula (1). 
                         
R is hydrogen, halogen, an alkyl group, an alkanoyl group, an aryl group, a heteroaryl group, or the like. X is oxygen, sulfur, selenium, or the like. Y and Z each is a bivalent group selected from a carbonyl group, a sulfinyl group, and a sulfonyl group. However, a case where Y and Z are both the carbonyl groups is excluded.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2015-059411, filed on Mar. 23, 2015; theentire contents of all of which are incorporated herein by reference.

FIELD

Embodiments disclosed herein relate generally to a polymer and a solarcell using the same.

BACKGROUND

An organic semiconductor is expected to be applied to a photoelectricconversion element such as an organic thin film solar cell, anorganic/inorganic hybrid solar cell, a light emitting element, and aphotosensor. Especially, using a high molecular compound as an organicsemiconductor material enables application of a low-cost coating methodin fabrication of an active layer. In view of an energy demand and anemission reduction of CO₂, a solar cell is expected as one of cleanenergies with low environmental burdens and its demand is rapidlyincreasing. A silicon-based solar cell is mainstream at present, butefficiency thereof is about 15%, and it is difficult to curtail a cost.A CdTe solar cell is also known as a solar cell which can be fabricatedat a low cost. However, since Cd being a toxic element is used, there isa possibility that an environmental problem occurs. Under thecircumstances, development of an organic thin film solar cell and anorganic/inorganic hybrid solar cell as a next-generation solar cellwhich is low in cost, high in energy conversion efficiency, and nontoxicis expected.

In order to put an organic thin film solar cell to practical use,improvement of power generation efficiency of the organic thin filmsolar cell is intensely demanded. In order to improve the powergeneration efficiency, improvement of an open circuit voltage (Voc) isimportant. A value of the open circuit voltage of the organic thin filmsolar cell greatly depends on a combination of an electron donor and anelectron acceptor, and materials used for them are required to beoptimized. It is known that the open circuit voltage of the organic thinfilm solar cell is correlated with a difference between an energy levelof a highest occupied molecular orbit (HOMO) of a p-type material and anenergy level of a lowest unoccupied molecular orbit (LUMO) of an n-typematerial. It is thought that, in an organic thin film solar cell whosedevelopment is currently in progress, fullerenes such asphenylC₆₁butyric acid methylester (PCBM) are most suitable as the n-typesemiconductor material. As a generally used p-type semiconductormaterial, a conjugated polymer of polythiophene such aspoly(3-hexylthiophene-2,5-diyl) (P3HT) can be cited.

The open circuit voltage (Voc) of the organic thin film solar cell usingthe combination of PCBM and P3HT is low, that is, about 0.6 V, and isnot necessarily satisfactory in view of practical use. A possible methodto improve a value of the open circuit voltage is to lower the HOMOlevel of the p-type semiconductor material. In this case, however, aband gap of the p-type semiconductor widens, which makes it impossibleto absorb light in a long wavelength range. That is, absorptionefficiency of light in a long wavelength side of a visible rangedecreases and thus entering light cannot be effectively used. As aresult, there is a drawback that energy efficiency does not increase.The open circuit voltage value and the absorption of the light in thelong wavelength range are often in a trade-off relation, and it isdifficult to achieve the both at higher level.

As one attempt to improve the open circuit voltage value of the organicthin film solar cell, using, as the p-type semiconductor material, apolymer in which imide is ring-condensed to thiophene is being studied.In the organic thin film solar cell using the polymer in which imide isring-condensed to thiophene as the p-type semiconductor, the opencircuit voltage improves to about 0.85 V, but power generationefficiency is 1% or less, and is required to be further improved. Theabove circumstances have led to a demand for a p-type semiconductormaterial which not only increases an open circuit voltage value of anorganic thin film solar cell but also improves an absorbingcharacteristic of light in a long wavelength range. Further, in anorganic thin film solar cell, improvement of life in addition toimprovement of the open circuit voltage is required. In order to improvethe life, active substances (a donor and an acceptor) excellent in heatstability and so on are required.

Further, researches have recently been made on an organic/inorganichybrid solar cell whose energy conversion efficiency is improved byusing an organic/inorganic hybrid perovskite compound or an inorganicperovskite compound for a photoelectric conversion layer. In theorganic/inorganic hybrid solar cell, polyarylamine or2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-bifluorene(spiro-OMeTAD)is used as a hole transport layer. Further, in order to enhanceconversion efficiency, a dopant such as t-butylpyridine (TBP) orbis(trifluoromethanesulfonyl)imidelithium (Li-TFSI) is used for the holetransport layer. However, since TBP is liquid and Li-TFSI is ahygroscopic substance, there occur performance deterioration caused bydiffusion or dissipation of TBP to the photoelectric conversion layerdue to a temperature increase, or by absorption of water molecules dueto deliquescence of Li-TFSI, and so on. This is a cause to shorten thelife of the organic/inorganic hybrid solar cell. It has been alsoproposed to use P3HT being a p-type material as the hole transportlayer, but sufficient power generation efficiency cannot be obtained inthis case.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a cross-sectional view showing a configuration of a solarcell of an embodiment.

DETAILED DESCRIPTION

According to one embodiment, there is provided a polymer having arepeating unit containing a bivalent group represented by the followingformula (1).

In the formula (1), R is a monovalent group selected from hydrogen,halogen, a cyano group, a nitro group, a substituted or unsubstitutedalkyl group, a substituted or unsubstituted alkanoyl group, asubstituted or unsubstituted aryl group, and a substituted orunsubstituted heteroaryl group, X is an atom selected from oxygen,sulfur, and selenium, the two Xs may be the same or may be different,and Y and Z are each independently a bivalent group selected from acarbonyl group, a sulfinyl group, and a sulfonyl group, with a casewhere Y and Z are both the carbonyl groups being excluded. Hereinafter,a polymer of an embodiment and a solar cell using the same will bedescribed.[First Polymer]

A first polymer in the embodiment is an organic high molecular compoundincluding a repeating unit represented by the following formula (2). Aweight-average molecular weight of the first polymer is preferably in arange of 3000 to 1000000.

In the formula (2), R is a monovalent group selected from hydrogen (H),halogen selected from fluorine (F), chlorine (Cl), bromine (Br), andiodine (I), a cyano group (—CN), a nitro group (—NO₂), a substituted orunsubstituted alkyl group, a substituted or unsubstituted alkanoylgroup, a substituted or unsubstituted aryl group, and a substituted orunsubstituted heteroaryl group. X is an atom selected from oxygen (O),sulfur (S), and selenium (Se). The two Xs may be the same or may bedifferent. Y and Z are each independently are a bivalent group selectedfrom a carbonyl group (—C(═O)—), a sulfinyl group (—S(═O)—), and asulfonyl group (—S(═O)₂—). A combination of Y and Z excludes a casewhere they are both the carbonyl groups.

In the R group, it is preferable that a carbon number of the substitutedor unsubstituted alkyl group is in a range of 1 to 30. The substitutedor unsubstituted alkyl group may be any one of straight-chained,branched-chained, and cyclic alkyl groups. As concrete examples of suchan alkyl group, there can be cited a methyl group, an ethyl group, apropyl group, an isopropyl group, a butyl group, a pentyl group, a hexylgroup, an octyl group, an isooctyl group, a 2-ethylhexyl group, a nonylgroup, a decyl group, a dodecyl group, an octadecyl group, a 2-hexadecylgroup, an octadodecyl group, a trifluoromethyl group, a pentafluoroethylgroup, a perfluorohexyl group, a perfluorooctyl group, and so on, butthe above alkyl group is not limited thereto.

In the R group, it is preferable that a carbon number of the substitutedor unsubstituted alkanoyl group (—C(═O)R1) is preferably in a range of 1to 30. The substituted or unsubstituted alkanoyl group may be any one ofstraight-chained, branched-chained, and cyclic alkanoyl groups. Asconcrete examples of the alkanoyl group, there can be cited an acetylgroup, a propanoyl group, a butanoyl group, a pentanoyl group, ahexanoyl group, an octanoyl group, a 2-ethylhexanoyl group, a nonanoylgroup, a decanoyl group, a dodecanoyl group, an octadecanoyl group, a2-hexadecanoyl group, an octadodecyl group, a trifluoroacetyl group, apentafluoropropanoyl group, a perfluorohexanoyl group, aperfluorooctanoyl group, and so on, but the above alkanoyl group is notlimited to these. An R1 group in the alkanoyl group is not limited to ansubstituted or unsubstituted alkyl group but may be halogen, an aromaticgroup, a heterocyclic group, and so on.

In the R group, carbon numbers of the substituted or unsubstituted arylgroup and heteroaryl group are preferably in a range of 4 to 20. Asconcrete examples of the aryl group and the heteroaryl group, a phenylgroup, a naphthyl group, a 4-biphenyl group, a 2-thienyl group, a2-furanyl group, a 4-tolyl group, a 4-octylphenyl group, a2-(5-ethylhexyl)thienyl group, a 2-(5-ethylhexyl)furanyl group, and soon can be cited, but the above aryl group and heteroaryl group are notlimited to these.

X in the formula (2) is an atom selected from oxygen (O), sulfur (S),and selenium (S). Y and Z are each a bivalent group selected from acarbonyl group (—C(═O)—), a sulfinyl group (—S(═O)—), and a sulfonylgroup (—S(═O)₂—). Y and Z may be the same groups or may be differentgroups. However, a combination where Y and Z are both the carbonylgroups is excluded. According to the organic high molecular compoundhaving a composite structure of a hetero five-membered ring and an imidefive-membered ring, which contains oxygen, sulfur, or selenium, with acarbonyl group of one of the imide rings being replaced by a sulfinylgroup or a sulfonyl group or with the carbonyl groups of the both imiderings being replaced by sulfinyl groups or sulfonyl groups, it ispossible to improve a light absorbing property while increasing an opencircuit voltage value of a solar cell.

In the polymer including the repeating unit represented by the formula(2), as the combination of Y and Z, a combination of the carbonyl groupand the sulfinyl group, the carbonyl group and the sulfonyl group, thesulfinyl group and the sulfonyl group, the sulfinyl group and thesulfinyl group, or the sulfonyl group and the sulfonyl group is employedas described above. Considering characteristics as a p-typesemiconductor material and fabrication easiness, among these, thecombination of the carbonyl group and the sulfinyl group and thecombination of the carbonyl group and the sulfonyl group are preferable,and the combination of the carbonyl group and the sulfonyl group is morepreferable.

The weight-average molecular weight of the polymer including therepeating unit represented by the formula (2) is in the range of 3000 to1000000, and in such a case, good solubility and semiconductorcharacteristics can be obtained. It is preferable that theweight-average molecular weight of the polymer is in a range of 10000 to600000. The weight-average molecular weight indicates a weight-averagemolecular weight of polystyrene conversion measured by a gel permeationchromatography method. Further, in order to impart good solubility tothe polymer, the R group is preferably a substituted or unsubstitutedalkyl group whose carbon number is 6 or more.

The repeating units represented by the formula (2) are sometimes bondedcyclically by themselves to constitute the polymer, but in general, therepeating unit includes end groups (Rt groups). As the end group Rt, amonovalent group similar to the aforesaid R is employed. The end groupRt may be a later-described cross-linking group. The first polymer inthe embodiment may be constituted only by the repeating unit representedby the formula (2), or may include a repeating unit other than thatrepresented by the formula (2). However, when the number of moles of therepeating unit represented by the formula (2) is less than 50 mol %, asemiconductor characteristic based on the repeating unit represented bythe formula (2) cannot be obtained sufficiently. Therefore, it ispreferable that a rate of the formula (2) is 50 mol % or more inrelation to the total number of moles of all the repeating units in thepolymer.

Concrete examples of the polymer including the repeating unitrepresented by the formula (2) are shown below. However, the firstpolymer of the embodiment is not limited to the concrete examples shownbelow. Note that, in the following formulas, Me is a methyl group, Et isan ethyl group, i-Pr is an isopropyl group, Bu is a butyl group, 2-EH isa 2-ethylhexyl group, Hex is a hexyl group, Oct is an octyl group, Hepis a heptyl group, 2-HecDec is a 2-hexyldecyl group, 2-OctDod is a2-octyldodecyl group, and Ph is a phenyl group.

[Second Polymer]

A second polymer in the embodiment is an organic high molecular compoundincluding a repeating unit represented by the following formula (3). Aweight-average molecular weight of the second polymer is preferably in arange of 3000 to 1000000.

The second polymer including the repeating unit represented by theformula (3) includes a substituted or unsubstituted bivalent conjugatedgroup Ar in addition to the repeating unit represented by the formula(2). In the repeating unit represented by the formula (3), the R group,X, Y, and Z each represent the same substituent or atom as that in theformula (2), and their concrete examples are also the same. In therepeating unit represented by the formula (3), the same parts as thosein the formula (2) are as described in the first polymer.

As concrete examples of the bivalent conjugated group Ar, those shownbelow can be cited. However, the conjugated group (conjugated linkinggroup) Ar is not limited to the following concrete examples.

The weight-average molecular weight of the polymer including therepeating unit represented by the formula (3) is in the range of 3000 to1000000, and in such a case, good solubility and semiconductorcharacteristics are obtained. The weight-average molecular weight of thepolymer is preferably in a range of 10000 to 600000. The repeating unitsrepresented by the formula (3) are sometimes cyclically bonded bythemselves to constitute the polymer, but in general, the repeating unitrepresented by the formula (3) includes end groups (Rt groups). The endgroup Rt is as previously described. The second polymer may beconstituted only by the repeating unit represented by the formula (3),or may include a repeating unit other than that represented by theformula (3). However, when the number of moles of the repeating unitrepresented by the formula (3) is less than 50 mol %, a semiconductorcharacteristic based on the repeating unit represented by the formula(3) cannot be obtained sufficiently. Therefore, it is preferable that arate of the formula (3) is 50 mol % or more in relation to the totalnumber of moles of all the repeating units in the polymer.

Concrete examples of the polymer including the repeating unitrepresented by the formula (3) are shown below. However, the secondpolymer of the embodiment is not limited to the concrete examples shownbelow.

[Third and Fourth Polymers]

A third polymer in the embodiment is an organic high molecular compoundincluding a structure represented by the following formula (2A). Afourth polymer in the embodiment is an organic high molecular compoundincluding a structure represented by the following formula (3A).Weight-average molecular weights of the third and fourth polymers arepreferably in a range of 3000 to 1000000.

The third and fourth polymers having the structures represented by theformula (2A) and the formula (3A) each have an R2 group and an R3 groupas end groups. At least one of the R2 group and the R3 group is asubstituent (monovalent group) having a cross-linking group. In theformula (2A) and the formula (3A), m is a positive number indicating apolymerization degree. By having the cross-linking group, the polymer,can have improved durability and so on. Note that the R2 group or the R3group not having the cross-linking group is the same as the R group. Inthe formula (2A) and the formula (3A), the R group, X, Y, Z, and Ar areeach the same substituent or atom as that in the formula (2) and theformula (3), and their concrete examples are also the same. In thestructures represented by the formula (2A) and the formula (3A), thesame parts as those in the formula (2) and the formula (3) are asdescribed in the first and second polymers.

It suffices that the cross-linking group is a substituent whichgenerates a cross-linking reaction by light, heat, or a radicalinitiator. For example, as a cross-linking group which generatescross-linking as a result that a bond is resolved by light, there can becited a substituent which includes an alkyl group or an alkoxy groupwhere substitution is carried out by bromine or iodine, a substituentwhich includes an azo group or a diazo group, and so on. Thecross-linking group may be a substituent which includes a double bond ora triple bond of carbon-carbon that generates photodimerization bylight, or a substituent which generates an addition reaction by heat. Assuch a cross-linking group, there can be exemplified an anthranyl group,a cinnamoyl group, a substituent which includes a coumarin structure, aphenylmaleimide group, a furfurylacrylate group, an acetylene group,benzocyclobutane, a cyclopentadienyl group, a substituent having abenzocyclobutane or a sultine structure, and so on. Further, thecross-linking group can be a substituent which includes a multiple bondof carbon-carbon, such as an acrylic group and a methacrylic group, as asubstituent which reacts with the radical initiator. Concrete examplesof the polymer having the cross-linking group are shown below. Thepolymer is not limited to the concrete examples below.

[Fifth and Sixth Polymers]

A fifth polymer in the embodiment is an organic high molecular compoundincluding a repeating unit represented by the following formula (4). Afifth polymer in the embodiment is an organic high molecular compoundincluding a repeating unit represented by the following formula (5).Weight-average molecular weights of the fifth and sixth polymers arepreferably in a range of 3000 to 1000000.

In the repeating unit represented by the formula (4), R′ is asubstituent (monovalent) having a cross-linking group. In the repeatingunit represented by the formula (5), at least one of R′ and Ar′ is asubstituent (a monovalent group or a bivalent group) having across-linking group. By having the cross-linking group, the polymer canhave improved durability and so on. The cross-linking group is asdescribed in the third and fourth polymers. In the formula (4) and theformula (5), R and R′ that does not have the cross-linking group areeach independently are a monovalent group selected from hydrogen,halogen, a cyano group, a nitro group, a substituted or unsubstitutedalkyl group, a substituted or unsubstituted alkanoyl group, asubstituted or unsubstituted aryl group, and a substituted orunsubstituted heteroaryl group. Concrete examples of these groups arepreviously described. X and X′ are each independently an atom selectedfrom oxygen, sulfur, and selenium. Y, Y′, Z, and Z′ are eachindependently a bivalent group selected from a carbonyl group, asulfinyl group, and a sulfonyl group. However, a case where Y and Z areboth the carbonyl groups and a case where Y′ and Z′ are both thecarbonyl groups are excluded. Concrete examples of these groups are aspreviously described. Ar and Ar′ that does not have the cross-linkinggroup are each a substituted or unsubstituted bivalent conjugated group.Concrete examples of these groups are as previously described. Concreteexamples of the repeating unit having the cross-linking group are shownbelow. However, the repeating units represented by the formula (4) andthe formula (5) are not limited to the following concrete examples.

[Method for Synthesizing Organic High Molecular Compound]

A method for synthesizing the polymer of the embodiment is not limitedin particular. The polymer of the embodiment can be synthesized as aresult that, for example, after monomers having functional groupssuitable for a polymerization reaction to be used are synthesized, themonomers are dissolved in an organic solvent as necessary andpolymerized by using a known aryl coupling reaction in which alkali, acatalyst, a ligand, and so on are used. As a polymerization method bythe aryl coupling reaction, there can be cited a polymerization methodby a Stille coupling reaction or a Suzuki coupling reaction, forinstance.

The polymerization by the Stille coupling is a method in which apalladium complex is used as the catalyst and the ligand is added asnecessary, and a monomer that has a trialkyltin residue is made to reactwith a monomer that has a halogen atom such as a bromine atom, an iodineatom, and a chlorine atom. As the palladium complex, there can be citedpalladium[tetrakis(triphenylphosphine)],[tris(dibenzylideneacetone)]dipalladium, palladiumacetate, andbis(triphenylphosphine)palladiumdichloride, for example. Details of thepolymerization by the Stille coupling reaction is described inInternational Publication No. 2010/008672, for example. As the solventused in the Stille coupling reaction, an organic solvent such astoluene, xylene, N,N-dimethylacetamide, N,N-dimethylformamide, and amixed solvent made by mixing two or more kinds of the above are used,for instance. The solvent used in the Stille coupling reaction is notlimited to these. In order to suppress a side reaction, it is preferablethat the solvent used in the Stille coupling reaction is subjected todeoxidization processing before the reaction.

The polymerization by the Suzuki coupling reaction is a method in which,under existence of an inorganic base or an organic base, a palladiumcomplex or a nickel complex is used as the catalyst, the ligand is addedas necessary, and a monomer that has a boronic acid residue or a boricacid ester residue is made to react with a monomer that has a halogenatom such as a bromine atom, an iodine atom, and a chlorine atom, or amonomer that has a sulfonate group such as a trifluoromethanesulfonategroup and a p-toluenesulfonate group.

As the inorganic base, there can be cited a sodium carbonate, apotassium carbonate, a cesium carbonate, a tripotassium phosphate, and apotassium fluoride, for example. As the organic base, there can be citeda tetrabutylammonium fluoride, a tetrabutylammonium chloride, atetrabutylammonium bromide, and a tetraethylammonium hydroxide, forexample. As the palladium complex, there can be citedpalladium[tetrakis(triphenylphosphine)],[tris(dibenzylideneacetone)]dipalladium, palladiumacetate, andbis(triphenylphosphine)palladiumdichloride, for example. As the nickelcomplex, bis(cyclooctadiene)nickel, for example, can be cited. As theligand, there can be cited triphenylphosphine,tri(2-methylphenyl)phosphine, tri(2-methoxyphenyl)phosphine,diphenylphosphinopropane, tri(cyclohexyl)phosphine, andtri(tert-butyl)phosphine, for example. Details of the polymerization bythe Suzuki coupling reaction is described in Journal of Polymer Science:Part A: Polymer Chemistry, Vol. 39, p 1533-1, 2001, for example.

In the polymerization by the aryl coupling reaction, a normal solvent isused. It suffices that the solvent is selected in consideration of apolymerization reaction to be used and solubilities of the monomers andthe polymer. Concretely, there can be cited an organic solvent such astetrahydrofuran, toluene, 1,4-dioxane, dimethoxyethane,N,N-dimethylacetamide, N,N-dimethylformamide, a mixed solvent made bymixing two or more kinds of the above, or a solvent having two phases ofan organic solvent phase and an aqueous phase. In the Suzuki couplingreaction, it is preferable to use an organic solvent such astetrahydrofuran, toluene, 1,4-dioxane, dimethoxyethane,N,N-dimethylacetamide, N,N-dimethylformamide, a mixed solvent made bymixing two or more kinds of the above, or a solvent having two phases ofan organic solvent phase and an aqueous phase. In order to suppress aside reaction, it is preferable that the solvent used in the Suzukicoupling reaction is subjected to deoxidization processing before thereaction.

In view of reactivity, a reaction temperature of the aryl couplingreaction is preferable to be −100° C. or more, more preferable to be−20° C. or more, and particularly preferable to be 0° C. or more. Inview of stability of the monomers and the high molecular compound, thereaction temperature is preferable to be 200° C. or less, morepreferable to be 150° C. or less, and particularly preferable to be 120°C. or less. In the polymerization by the aryl coupling reaction, a knownmethod can be applied to extraction of the polymer from a reactionsolution after the reaction. For example, the polymer of the embodimentcan be obtained as a result that the reaction solution is added to alower alcohol such as methanol, that a precipitated deposit is filtered,and that a filtered material is dried. When purity of the obtainedpolymer is low, the polymer may be refined by recrystallization,continuous extraction by a Soxhlet extractor, column chromatography, orthe like.

The polymer of the embodiment can be synthesized by using the Stillecoupling reaction. For example, the polymer is synthesized bypolymerizing a dihalogen compound represented by a formula (6) andbis(trialkyl)tin represented by a formula (7). In the followingformulas, the R group, X, Y, Z are as previously described. L is ahalogen atom selected from fluorine (F), chlorine (Cl), bromine (Br),and iodine (I). R″ is, for example, an alkyl group such as a methylgroup, an ethyl group, a propyl group, a butyl group, or an octyl group.

Concrete examples of the compound represented by the formula (6) areshown below. However, the compound is not limited to the followingconcrete examples.

Structure examples of the compound represented by the formula (7) areshown below. However, the compound is not limited to the followingstructure examples.

Concrete examples of the compound represented by the formula (7) areshown below. However, the compound is not limited to the followingconcrete examples.

The polymer of the embodiment may have the previously describedcross-linking group. In such a case, the polymer is synthesized by usinga compound having the cross-linking group. A structure example of thecompound having the cross-linking group is shown below. However, thecompound is not limited to the following structure example. In theformula below, R2 and R3 are each a substituent having the cross-linkinggroup. X, Y, and Z are as previously described. L is a halogen atomselected from fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).R″ is an alkyl group such as, for example, a methyl group, an ethylgroup, a propyl group, a butyl group, or an octyl group.R₂-LR₃-LR₂—SnR″₃R₃—SnR″₃

Concrete examples of the compound having the cross-linking group areshown below. However, the compound is not limited to the followingconcrete examples.

The polymer of the embodiment can be synthesized by using the Suzukicoupling reaction. The polymer is synthesized by polymerizing thecompound represented by the formula (6) and a compound represented by aformula (8), for instance. In the following formulas, Q is a boric acidester residue and means a group which is boric acid diester from which ahydroxy group is removed. Concrete examples of the Q group are shownbelow but the Q group is not limited to these. In the formulas, Me is amethyl group and Et is an ethyl group.Q-Ar-Q  (8)

[Solar Cell]

A solar cell of an embodiment includes a photoelectric conversionelement which has a pair of electrodes and a photoelectric conversionlayer disposed therebetween and containing an organic material. Aslayers containing the organic material out of layers forming thephotoelectric conversion layer, an active layer, a buffer layer, and soon can be cited. As the active layer containing the organic material,for example, a layer having a p-type semiconductor material (electrondonor) containing the aforesaid polymer of the embodiment and an n-typesemiconductor material (electron acceptor) can be cited. Thephotoelectric conversion element including the photoelectric conversionlayer containing such an organic material is applicable not only to asolar cell but also to a photosensor and a light emitting element.

[Organic Thin Film Solar Cell]

The solar cell of the embodiment will be described with reference to TheFIGURE. A solar cell element 100 shown in The FIGURE has a substrate110, a first electrode 120, a photoelectric conversion layer 130, and asecond electrode 140. The FIGURE shows a solar cell element(photoelectric conversion element) used for a normal organic thin filmsolar cell, but a structure of the solar cell element is not limitedthereto. The photoelectric conversion layer 130 has a first buffer layer131, an active layer 132, and a second buffer layer 133. The bufferlayers 131, 133 are disposed when necessary. The first electrode 120 isan electrode (hereinafter, sometimes referred to as a cathode) tocollect an electron. The second electrode 140 is an electrode(hereinafter, sometimes referred to as an anode) to collect a hole. InThe FIGURE, the cathode 120 is disposed on a substrate 110 side, but thecathode 120 and the anode 140 can be reversed. These parts will bedescribed.

<Active Layer (132)>

The active layer 132 in the solar cell element 100 of the embodimentincludes the p-type semiconductor material (electron donor) and then-type semiconductor material (electron acceptor). The p-typesemiconductor material has the aforesaid polymer of the embodiment. Aconcrete configuration of the polymer as the p-type semiconductormaterial is as described above. The n-type semiconductor material(electron acceptor) will be described below. The active layer 132 caninclude a plurality of kinds of p-type semiconductor materials, andsimilarly, can include a plurality of kinds of n-type semiconductormaterials.

<n-Type Semiconductor Material>

As the n-type semiconductor material (electron acceptor) included in theactive layer 132, there can be cited a phthalocyanine derivative, afullerene or a fullerene derivative, a boron-containing polymer,poly(benzobisimidazobenzophenanthroline), and so on, but the n-typesemiconductor material included in the active layer 140 is not limitedthereto. Among the above, the fullerene derivative is preferable. Asconcrete examples of the fullerene derivative, there can be cited1′,1″,4′4″-Tetrahydro-di[1,4]methanonaphthaleno[1,2:2′,3′,56,60:2″,3″][5,6]fullerene-C60(indene-C₆₀bis adduct: IC60BA), [6,6]-Phenyl C61 butyric acid methylester (PC60BM), [6,6]-Phenyl C71 butyric acid methyl ester (PC70BM),Dihyrdonaphtyl-based[60]fullerene bisadducts (NC60BA),Dihyrdonaphtyl-based[70]fullerene bisadducts (NC70BA), and so on, butthe fullerene derivative is not limited thereto.

<Configuration and Structure of Active Layer>

In order to transfer an electron from the electron donor (p-typesemiconductor) to the electron acceptor (n-type semiconductor)efficiently, a relativity between LUMO energy levels of the p-typesemiconductor material and the n-type semiconductor material isimportant. Concretely, it is preferable that the LUMO energy level ofthe p-type semiconductor material is higher than the LUMO energy levelof the n-type semiconductor material by a predetermined energy. In otherwords, it is preferable that electron affinity of the p-typesemiconductor material is larger than electron affinity of the n-typesemiconductor material by the predetermined energy.

If the LUMO energy level of the n-type semiconductor material is toohigh, the transfer of the electron is hard to occur, and thus ashort-circuit current (Jsc) of the solar cell element 100 tends tobecome low. On the other hand, an open circuit voltage (Voc) of thesolar cell element 100 is determined by a difference between a HOMOenergy level of the p-type semiconductor material and the LUMO energylevel of the n-type semiconductor material. Therefore, if the LUMOenergy level of the n-type semiconductor material is too low, the Voctends to become low. That is, in order to realize higher conversionefficiency, it is not enough to simply select the n-type semiconductormaterial whose LUMO energy level is high or whose LUMO energy level islow.

It is possible to adjust the LUMO energy level of the aforementionedfifth polymer of the embodiment by selecting its substituent. That is,as a result of changing substituents of two kind of monomersconstituting a copolymer, compounds having various energy levels can beobtained. In order to obtain the monomers having various substituents, aknown technique such as esterification, etherification, andcross-coupling, for example, can be used. However, a suitablecombination of the p-type semiconductor material and the n-typesemiconductor material is not simply determined only based on the LUMOenergy level and the HOMO energy level.

In the solar cell element 100, light is absorbed by the active layer132, charge separation occurs in an interface between the p-typesemiconductor and the n-type semiconductor, and an electron and a holewhich have been generated are extracted from the electrodes 120, 140. Athickness of the active layer 132 is not limited in particular, but thethickness of the active layer 132 is preferable to be from 10 nm to 1000nm, and is further preferable to be from 50 nm to 250 nm. By setting thethickness of the active layer 132 to 10 nm or more, uniformity of thelayer is maintained and a short circuit becomes hard to occur. Bysetting the thickness of the active layer 132 to 1000 nm or less, aninternal resistance can be made small, and as a result that a distancebetween the electrodes 120, 140 becomes closer, diffusion of electriccharges are made better.

As concrete structures of the active layer 132, there can be cited athin film laminated type in which a p-type semiconductor layer and ann-type semiconductor layer are laminated, and a bulk hetero junctiontype in which a p-type semiconductor material and an n-typesemiconductor material are mixed. The active layer 132 of the thin filmlaminated type may have a layer (i layer) which is disposed between thep-type semiconductor layer and the n-type semiconductor layer and inwhich the p-type semiconductor material and the n-type semiconductormaterial are mixed. It is preferable that the solar cell element 100 ofthe embodiment has the active layer 132 including the bulk heterojunction structure in which the p-type semiconductor material and then-type semiconductor material are mixed.

The bulk hetero junction type active layer 132 includes the p-typesemiconductor material and the n-type semiconductor material. In theactive layer 132, a p-type semiconductor phase and an n-typesemiconductor phase are phase-separated from each other. When the activelayer 132 absorbs light, a negative charge (electron) and a positivecharge (hole) are separated in the interface of these phases andtransported to the electrodes 120, 140 through the respectivesemiconductors. In the bulk hetero junction type active layer 132, thephase separation structure of the p-type semiconductor phase and then-type semiconductor phase affects a light absorption process, adiffusion process of excitons, a dissociation process of the excitons(charge generation process), a carrier transportation process, and soon. Therefore, in order to heighten photoelectric conversion efficiencyof the solar cell element 100, it is preferable to make the phaseseparation structure of the p-type semiconductor phase and the n-typesemiconductor phase in the active layer 132 appropriate.

<Forming Method of Active Layer>

A forming method of the active layer 132 is not limited in particular,but it is preferable to apply a wet coating method such as a spin coatmethod, an ink-jet method, a doctor blade method, and a drop castingmethod. In this case, a solvent is selected in which the p-typesemiconductor material (the aforesaid polymer of the embodiment) and then-type semiconductor material are soluble, and a coating solution whichincludes the p-type semiconductor material made of the polymer and then-type semiconductor material is fabricated. By applying this coatingsolution, the bulk hetero junction type active layer 132 can be formed.

A kind of the solvent is not limited in particular as long as thesemiconductor materials can be dissolved in the solvent uniformly. Thesolvent can be selected, for example, from aliphatic hydrocarbons suchas hexane, heptane, octane, isooctane, nonane, and decane, aromatichydrocarbons such as toluene, xylene, chlorobenzene, andorthodichlorobenzene, low alcohols such as methanol, ethanol, andpropanol, ketones such as acetone, methyl ethyl ketone, cyclopentanone,and cyclohexanone, esters such as ethyl acetate, butyl acetate, andmethyl lactate, halogen hydrocarbons such as chloroform, methylenechloride, dichloroethane, trichloroethane, and trichloroethylene, etherssuch as ethyl ether, tetrahydrofuran, and dioxane, amides such asdimethylformamide and dimethylacetamide, and so on.

<Additive to Active Layer Coating Solution>

In a case where the bulk hetero junction type active layer 132 is to beformed by the coating method, addition of a compound with a lowmolecular weight to the coating solution sometimes improvesphotoelectric conversion efficiency. As a mechanism where the additiveoptimizes a phase separation structure and improves the photoelectricconversion efficiency, a plurality of causes can be considered. As oneof the causes, it is considered that existence of the additivesuppresses aggregation of the p-type semiconductor materials to eachother or of the n-type semiconductor materials to each other. In otherwords, without the additive, the solvent of the active layer coatingsolution (ink) normally volatilizes immediately after the coating. It isconsidered that the p-type semiconductor material and the n-typesemiconductor material which remain as residual components on thisoccasion each form a large aggregate. In such a case, a joint area (areaof the interface) between the p-type semiconductor material and then-type semiconductor material becomes small, and charge generationefficiency is lowered.

When the ink which includes the additive is applied, the additiveremains for a while after the volatilization of the solvent. In otherwords, since the additive exists in the p-type semiconductor material orin the n-type semiconductor material, or in peripheries of the both,aggregation of the p-type semiconductor material and/or the n-typesemiconductor material is prevented. It is considered that the additiveevaporates at a low speed under a room temperature and a normal pressureafter the application of the ink. The p-type semiconductor material andthe n-type semiconductor material are considered to aggregate as theadditive evaporates, but since the remaining additive prevents theaggregation, the aggregates which the p-type semiconductor material andthe n-type semiconductor material form are smaller. Consequently, in theactive layer 132, a phase separation structure is formed in which thejoint area of the p-type semiconductor material and the n-typesemiconductor material is large and which has higher charge generationefficiency.

As described above, it is preferable that the additive remains in theactive layer 132 for a while after the volatilization of the mainsolvent of the ink. From such a viewpoint, it is preferable that aboiling point of the additive is higher than that of the main solvent ofthe ink. Since boiling points of chlorobenzene and orthodichlorobenzene,which are often used as main solvents of ink, are 131° C. and 181° C.respectively, it is preferable that the boiling point of the additiveunder the normal pressure (1000 hPa) is higher than the above. From asimilar viewpoint, it is preferable that a vapor pressure of theadditive is lower than a vapor pressure of the main solvent of the inkunder the room temperature (25° C.). If the boiling point of theadditive is too high, the additive does not disappear completely fromthe active layer 132 after fabrication of the element, and it issupposed that an amount of the additive remaining in the active layer132 increases. In such a case, it is considered that increase ofimpurities causes reduction of mobility, that is, reduction of thephotoelectric conversion efficiency. Therefore, it can also be said thatthe boiling point of the additive is preferably not too high.

The boiling point of the additive under the normal pressure ispreferable to be higher than the boiling point of the main solvent by arange of 10° C. or more to 200° C. or less, and further, is morepreferable to be higher than the boiling point of the main solvent by arange of 50° C. or more to 100° C. or less. If the boiling point of theadditive is too low, the aggregation of the n-type semiconductormaterial is apt to occur at a time of drying of the ink. Consequently,morphology of the active layer 132 becomes large, and there is apossibility that a surface becomes uneven. It is preferable that theadditive is liquid under the room temperature (25° C.), in view offacilitating ink fabrication. If the additive is solid under the roomtemperature, it is considered that dissolving the additive in the mainsolvent at the time of the ink fabrication is difficult or that a longstirring time is required even if the additive can be dissolved. Inorder to optimize the phase separation structure of the active layer132, not only the boiling point of the additive but also compatibilityof the additive with the p-type semiconductor material and the n-typesemiconductor material is also important. In other words, since theadditive interacts with the p-type semiconductor material and the n-typesemiconductor material, there is a possibility that crystallinity or thelike of the p-type semiconductor material or the n-type semiconductormaterial changes depending on a structure of the additive, for example.

As concrete examples of the additive, there can be cited an aromaticcompound such as alkane having a substituent and naphthalene having asubstituent. As the substituent, there can be cited an aldehyde group,an oxo group, a hydroxy group, an alkoxy group, a thiol group, athioalkyl group, a carboxyl group, an ester group, an amine group, anamide group, a fluoro group, a chloro group, a bromo group, an iodinegroup, a nitrille group, an epoxy group, an aryl group, and so on. Thesubstituent may be single or may be plural. As the substituent whichalkane has, the thiol group or the iodine group is preferable. As thesubstituent which the aromatic compound such as naphthalene has, thebromo group or the chloro group is preferable. Since it is preferablethat the additive has the high boiling point as described above, acarbon number of alkane is preferable to be 6 or more, and is morepreferable to be 8 or more. Since it is preferable that the additive isliquid under the room temperature as described above, the carbon numberof the alkane is preferable to be 14 or less and further preferable tobe 12 or less.

It is preferable that an amount of the additive included in the ink(active layer coating solution) is 0.1 wt % or more to 10 wt % or lessin relation to the entire ink. Further, it is more preferable that theabove amount is 0.5 wt % or more to 3 wt % or less in relation to theentire ink. By setting the amount of the additive in such a range, apreferable phase separation structure can be obtained while the additiveremaining in the active layer 132 is decreased.

Electrodes (120, 140)>

The electrodes 120, 140 in the solar cell element 100 of the embodimenthave a function to collect an electron or a hole generated as a resultof absorption of light by the active layer 132. Therefore, it ispreferable that the first electrode 120 is suitable for collection ofthe election, and it is preferable that the second electrode 140 issuitable for collection of the hole. It is preferable that at least oneof the pair of electrodes 120, 140 has a light transmitting property,and the both may have the light transmitting properties. Having thelight transmitting property means that 40% or more of sunlight istransmitted. It is more preferable that the electrode having the lighttransmitting property transmits 70% or more of sunlight, and therebylight is easily transmitted through a transparent electrode to reach theactive layer 132. A transmittance of light can be measured by a commonspectrophotometer, and indicates an average transmittance of visiblelight (400 nm to 800 nm), for example.

<Electrode (120) Suitable for Collection of Electron>

The electrode (cathode) 120 suitable for collection of an electron isgenerally an electrode constituted by a conductive material exhibiting alower value of a work function than the anode 140. According to such acathode 120, the electron generated in the active layer 132 can beextracted smoothly. As forming materials of the cathode 120, used are,for example, a metal such as lithium, sodium, potassium, cesium,calcium, and magnesium, an alloy thereof, an inorganic salt such as alithium fluoride and a cesium fluoride, and a metal oxide such as anickel oxide, an aluminum oxide, a lithium oxide, and a cesium oxide.These materials are materials having low work functions, and thus aresuitable as the materials for the cathode 120. Further, between thecathode 120 and the active layer 132, the buffer layer 131 formed of ann-type semiconductor having conductivity can be provided. In such acase, as the forming material of the cathode 120, a material having ahigh work function may be used.

In a case where the cathode 120 is a transparent electrode, usable are,for example, a conductive metal oxide such as a nickel oxide, a tinoxide, an indium oxide, an indium tin oxide (ITO), a fluorine-doped tinoxide (FTO), an indium-zirconium oxide (IZO), a titanium oxide, and azinc oxide, and a composite body or a laminated body of a metal nanowireof gold, silver, copper, or the like, or a carbon nanotube (CNT) and aconductive metal oxide, and it is especially preferable to use ITO.

A film thickness of the cathode 120 is not limited in particular, butthe film thickness is preferable to be 10 nm or more to 1 μm or less andis further preferable to be 50 nm or more to 300 nm or less. If the filmthickness of the cathode 120 is too thin, a sheet resistance becomeshigh, and if the film thickness of the cathode 120 is too thick, a lighttransmittance is lowered. In a case where the cathode 120 is thetransparent electrode, it is preferable to select the film thickness sothat both a high light transmittance and a low sheet resistance can beobtained. The sheet resistance of the cathode 120 is not limited inparticular, but is preferable to be 500Ω/□ or less, more preferable tobe 200Ω/□ or less, and normally is 1Ω/□ or more. In view of extracting alarger current, it is preferable that the sheet resistance is small. Asforming methods of the cathode 120, there can be cited a vacuum filmforming method such as vapor deposition and sputtering, a method offorming a film by applying an ink containing a nano-particle or aprecursor, and so on.

<Electrode (140) Suitable for Collection of Hole>

The electrode (anode) 140 suitable for collection of the hole isgenerally an electrode constituted by a conductive material exhibiting ahigher value of a work function than the cathode 120. Such an anode 140can extract the hole generated in the active layer 132 smoothly. As aforming material of the anode 140, usable is, for example, a metal suchas platinum, gold, silver, copper, nickel, cobalt, iron, manganese,tungsten, titanium, zirconium, tin, zinc, aluminum, indium, or chromium,or an alloy thereof. These materials have high work functions, and thusare suitable as the materials for the anode 140.

The aforesaid materials each can be laminated with a conductive highmolecular material represented by PEDOT/PSS which is a polythiophenederivative doped with polystyrenesulfonate, or laminated with a metaloxide having a high work function such as a molybdenum oxide, a vanadiumoxide, a nickel oxide, or a copper oxide. For example, it is possible toprovide the buffer layer 133 constituted by the conductive highmolecular material or the metal oxide between the anode 140 and theactive layer 132. When laminating the conductive high molecular materialor the metal oxide, a metal suitable for the anode 140 such as aluminumand magnesium can be used instead of the above-described material havingthe high work function, since a work function of the conductive highmolecular material is high. It is also possible to use the conductivehigh molecular material itself as the material for the anode 140. As theconductive high molecular material, there can be cited theaforementioned PEDOT/PSS, a material made by doping polypyrrole,polyaniline, or the like with iodine or the like, and so on. In a casewhere the anode 140 is the transparent electrode, the aforesaidconductive metal oxide or the like is used.

A film thickness of the anode 140 is not limited in particular, but thefilm thickness is preferable to be 10 nm or more to 10 μm or less and isfurther preferable to be 50 nm or more to 500 nm or less. If the filmthickness of the anode 140 is too thin, a sheet resistance becomes high,and if the film thickness is too thick, a light transmittance islowered. In a case where the anode 140 is the transparent electrode, itis preferable to select the film thickness so that both a high lighttransmittance and a low sheet resistance can be obtained. The sheetresistance of the anode 140 is not limited in particular, but preferableto be 500Ω/□ or less and more preferable to be 200Ω/□ or less. The sheetresistance is normally 1Ω/□ or more. In view of extracting a largercurrent, it is preferable that the sheet resistance is small. As formingmethods of the anode 140, there can be cited a vacuum film formingmethod such as vapor deposition and sputtering, a method of forming afilm by applying an ink containing a nano-particle or a precursor, andso on.

<Buffer Layer (131, 133)>

The solar cell element 100 of the embodiment can have, in addition tothe pair of electrodes 120, 140 and the active layer 132 disposedtherebetween, one or more buffer layer(s). The buffer layers can beclassified into the electron extraction layer 131 and the holeextraction layer 133. In a case where the first electrode 120 is acathode and the second electrode 140 is an anode, the electronextraction layer 131 is disposed between the active layer 132 and thecathode 120, and the hole extraction layer 133 is disposed between theactive layer 132 and the anode 140.

<Electron Extraction Layer (131)>

A material for the electron extraction layer 131 is not limited inparticular as long as the material enables improvement of efficiency ofextraction of the electron from the active layer 132 to the cathode 120.The forming materials for the electron extraction layer 131 are roughlycategorized into an inorganic compound and an organic compound. Theelectron extraction layer 131 may be formed by using the material ofonly either one category of the above, or may be formed by using thematerials of both categories. It is possible to use a laminated body ofan inorganic compound layer and an organic compound layer as theelectron extraction layer 131.

As the inorganic compound material used for the electron extractionlayer 131, a salt of an alkali metal such as lithium, sodium, potassium,and cesium, and an n-type oxide semiconductor compound such as atitanium oxide (TiO_(x)) and a zinc oxide (ZnO) are preferable. As thesalt of the alkali metal, a fluoride salt such as a lithium fluoride, asodium fluoride, a potassium fluoride, and a cesium fluoride ispreferable. By using such a material, when it is used in combinationwith the cathode 120 made of aluminum or the like, it is possible tomake a work function of the cathode 120 small and to raise a voltageapplied to the inside of the solar cell element 100.

When the alkali metal salt is used as the forming material for theelectron extraction layer 131, a vacuum film forming method such asvacuum deposition and sputtering can be applied to form the electronextraction layer 131. Among the above, it is desirable to form theelectron extraction layer 131 by vacuum deposition by resistanceheating. Usage of the vacuum deposition can make damage to the otherlayers such as the active layer 132 smaller. A film thickness in such acase is preferable to be 0.1 nm or more to 50 nm or less, and is morepreferable to be 20 nm or less. If the electron extraction layer 131 istoo thin, an effect to improve efficiency of extraction of an electronbecomes insufficient. If the electron extraction layer 131 is too thick,there is a possibility that a property of the element is impaired by theelectron extraction layer 131 acting as a series resistance component.

When the titanium oxide is used as the forming material for the electronextraction layer 131, a vacuum film forming method such as a sputteringmethod can be applied to form the electron extraction layer 131.However, it is more preferable that the electron extraction layer 131made of the titanium oxide is formed by a coating method. For example,it is possible to form the electron extraction layer 131 constituted bythe titanium oxide by a sol gel method described in Adv. Mater. 18, 572(2006). The film thickness in that case is normally 0.1 nm or more to100 nm or less, and is preferable to be 5 nm or more to 50 nm or less.If the electron extraction layer 131 is too thin, an effect to improvethe efficiency of extraction of the electron becomes insufficient. Ifthe electron extraction layer 131 is too thick, there is a possibilitythat a property of the element is impaired by the electron extractionlayer 131 acting as a series resistance component.

In a case where the zinc oxide is used as the forming material for theelectron extraction layer 131, the formation can also be performed byusing a vacuum film forming method such as a sputtering method, but itis preferable to form the electron extraction layer 131 by using acoating method. For example, according to a sol gel method described inSol-Gel Science, C. J. Brinker, G. W. Scherer, Academic Press (1990),the electron extraction layer 131 constituted by the zinc oxide can beformed. The film thickness in that case is normally 0.1 nm or more to400 nm or less, and is preferable to be 1 nm or more to 50 nm or less.If the electron extraction layer 131 is too thin, an effect to improveefficiency of extraction of an electron becomes insufficient. If theelectron extraction layer 131 is too thick, there is a possibility thata property of the element is impaired by the electron extraction layer131 acting as a series resistance component.

As the organic compound material used as the electron extraction layer131, there can be cited, for example, bathocuproine (BCP), bathophenanthrene (Bphen), (8-hydroxyquinolinato)aluminum (Alq3), a boroncompound, an oxadiazole compound, a benzoimidazole compound, anaphthalenetetracarboxylic acid anhydride (NTCDA), aperylenetetracarboxylic acid anhydride (PTCDA), a phosphineoxidecompound, a phosphinesulfide compound, etc., and a conductive polymer,but the organic compound material used as the electron extraction layer131 is not limited thereto. The above-described organic compoundmaterial may be doped with a metal such as an alkali metal and analkaline earth metal.

When the organic compound is used as the forming material for theelectron extraction layer 131, a film thickness of the electronextraction layer 131 is normally 0.5 nm or more to 500 nm or less, andis preferable to be 1 nm or more to 100 nm or less. If the electronextraction layer 131 is too thin, an effect to improve efficiency ofextraction of an electron becomes insufficient. If the electronextraction layer 131 is too thick, there is a possibility that aproperty of the element is impaired by the electron extraction layer 131acting as a series resistance component. If the electron extractionlayer 131 is formed by using a plurality of materials, an entirethickness of the electron extraction layer 131 is normally 0.1 nm ormore to 100 nm or less, and is preferable to be 60 nm or less.

<Hole Extraction Layer (133)>

A material for the hole extraction layer 133 is not limited inparticular as long as the material enables improvement of efficiency ofextraction of the hole from the active layer 132 to the anode 140.Concretely, there can be cited a conductive polymer made by dopingpolythiophene, polypyrrole, polyacetylene,triphenylenediaminepolypyrrol, polyaniline or the like with at least onedoping material out of sulfonic acid and iodine. Among the above, theconductive polymer doped with the sulfonic acid is preferable, andfurther, PEDOT:PSS made by doping a polythiophene derivative withpolystyrenesulfonic acid is more preferable. A metal oxide having a highwork function such as a tungsten oxide and a molybdenum oxide can beused as the hole extraction layer 133. A thin film of a metal such asgold, indium, silver, and palladium can be also used as the holeextraction layer 133. The metal thin film may be used independently asthe hole extraction layer 133 It is also possible to combine the metalthin film and the above-described conductive polymer to use thecombination as the hole extraction layer 133.

A film thickness of the hole extraction layer 133 is not limited inparticular, but normally the film thickness thereof is 1 nm or more to200 nm or less. The film thickness of the hole extraction layer 133 ispreferable to be 5 nm or more and preferable to be 100 nm or less. Ifthe film thickness of the hole extraction layer 133 is too thin,uniformity becomes insufficient and there is a tendency that a shortcircuit occurs. If the film thickness of the hole extraction layer 133is too thick, a resistance value is increased and there is a tendencythat the hole is hard to be extracted.

<Forming Method of Buffer Layers>

A forming method of the buffer layers 131, 133 is not limited inparticular. Film forming methods for several materials are as describedabove. Generally, when a material having sublimability is used, a vacuumfilm forming method such as a vacuum deposition method can be used. Whena material soluble in a solvent is used, a wet coating method such asspin-coating and ink-jetting can be used.

<Substrate (110)>

The solar cell element 100 normally has the substrate 110 being asupporter. That is, the electrodes 120, 140, the active layer 132, andthe buffer layers 131, 133 are formed on the substrate 110. A materialfor the substrate 110 is not limited in particular. As the substratematerials, there can be cited an inorganic material such as quartz,glass, sapphire, and titania, an organic material such as polyethyleneterephthalate, polyethylenenaphthalate, polyethersulfone, polyimide,nylon, polystyrene, a polyvinyl alcohol, an ethylene-vinyl alcoholcopolymer, a fluorocarbon resin, a vinyl chloride, polyolefin such aspolyethylene, cellulose, a polyvinylidene chloride, aramid, apolyphenylene sulfide, polyurethane, polycarbonate, polyarylate,polynorbornene, and an epoxy resin, a paper material such as paper andsynthetic paper, a composite material made by applying or laminating alayer which gives insulation performance on a metal such as stainlesssteel, titanium, aluminum, and so on. As the glass, soda glass, blueplate glass, no-alkali glass, and so on can be cited. With regard to aquality of the material of the glass, since fewer eluted ions arebetter, the no-alkali glass is preferable.

A shape of the substrate 110 is not limited and a shape of board, film,sheet, or the like can be used, for example. A thickness of thesubstrate 110 is not limited in particular, either. The thickness of thesubstrate 110 is normally 5 μm or more to 20 mm or less, and ispreferable to be 20 μm or more to 10 mm or less. If the substrate 110 istoo thin, there is a possibility that strength of the solar cell element100 is insufficient, and if the substrate 110 is too thick, there is apossibility that a cost becomes high or a weight becomes too heavy. In acase where the substrate 110 is of glass, excessive thinness reducesmechanical strength and makes the substrate 110 easy to crack, and thusthe thickness thereof is preferable to be 0.01 mm or more and morepreferable to be 0.1 mm or more. Further, excessive thickness makes thesubstrate 110 heavy, and thus the thickness of the substrate 110 ispreferable to be 10 mm or less, and is more preferable to be 3 mm orless.

<Method for Manufacturing Solar Cell Element 100>

The solar cell element 100 of the embodiment can be fabricated bysequentially forming the electrode 120, the photoelectric conversionlayer 130, and the electrode 140 on the substrate 110 by theaforementioned method. When the buffer layers 131, 133 are to beprovided, the electrode 120, the buffer layer 131, the active layer 132,the buffer layer 133, and the electrode 140 are sequentially formed onthe substrate 110. Further, it is preferable that a heat treatment(annealing treatment) is performed to a laminated body obtained bysequentially forming these layers on the substrate 110. By performingthe annealing treatment, heat stability and durability of the solar cellelement 100 sometimes improve. The annealing treatment sometimesimproves adhesion between the layers, which is considered to be one ofthe reasons for the above.

A heating temperature is normally 200° C. or less, is preferable to be180° C. or less, and is more preferable to be 150° C. or less. Theheating temperature is normally 50° C. or more, and is preferable to be80° C. or more. If the temperature is too low, there is a possibilitythat an improvement effect of the adhesion cannot be obtainedsufficiently. If the temperature is too high, there is a possibilitythat the compound included in the active layer 132 is thermallydecomposed, for example. Note that heating at a plurality oftemperatures may be applied to the annealing treatment. A heating timeis normally 1 minute or more to 3 hours or less, and is preferable to be3 minutes or more to 1 hour or less. It is preferable that the annealingtreatment is terminated when an open circuit voltage, a short-circuitcurrent, and a fill factor, which are parameters for solar cellperformance, reach predetermined values. The annealing treatment ispreferable to be performed under a normal pressure, and is alsopreferable to be performed in an inert gas atmosphere.

The solar cell of the embodiment can be fabricated by using an arbitrarymethod. For example, according to a known technique, a surface of theorganic thin film solar cell (solar cell element 100) is covered by anappropriate protective material in order for improvement of weatherresistance, and thereby the solar cell can be fabricated. As theprotective material, there can be cited a weather-resistant protectivefilm, an ultraviolet cutting film, a gas barrier film, a getter materialfilm, a sealant, and so on. It is possible to add a known configurationother than the above.

[Organic/Inorganic Hybrid Solar Cell]

Next, another example of the solar cell of the embodiment will bedescribed. Here, an example where the solar cell of the embodiment isapplied to an organic/inorganic hybrid solar cell will be described. Theorganic/inorganic hybrid solar cell has, for example, a laminatedstructure (inverse structure) of substrate/cathode electrode/electronextraction layer/active layer/hole extraction layer/anode electrode.Positions of the cathode electrode and the anode electrode may bereversed.

As the active layer of the organic/inorganic hybrid solar cell, anorganic/inorganic hybrid perovskite compound is used. Further, as thehole extraction layer of the organic/inorganic hybrid solar cell, ap-type semiconductor material is used. The p-type semiconductor materialforming the hole extraction layer contains the polymer of the embodimentdescribed above. A concrete structure of the polymer as the p-typesemiconductor material is as previously described. The hole extractionlayer may contain a plurality of kinds of p-type semiconductormaterials.

In the organic/inorganic hybrid solar cell, as a result that irradiatinglight is absorbed in the active layer containing the organic/inorganichybrid perovskite compound, charge separation occurs in the activelayer. An electron generated by the charge separation is extracted fromthe cathode electrode, and a hole is extracted from the anode electrode.In the organic/inorganic hybrid solar cell, buffer layers (the electronextraction layer and the hole extraction layer) similar to those of theorganic thin film solar cell are usable. The organic/inorganic hybridsolar cell is fabricated by the same method as the above-describedmethod for the organic thin film solar cell.

The organic/inorganic hybrid perovskite compound used for the activelayer of the organic/inorganic hybrid solar cell has a compositionrepresented by the following formula (28), for instance.CH₃NH₄ML₃.  (28)In the formula (28), M is at least one atom selected from a groupconsisting of lead (Pb) and tin (Sn), and L is at least one atomselected from a group consisting of iodine (I), bromine (Br), andchlorine (Cl).

As a method for fabricating the active layer, there can be cited amethod of vacuum-depositing the aforesaid perovskite compound or itsprecursor, and a method in which a solution in which the perovskitecompound or its precursor is dissolved in a solvent is applied, followedby heating and drying. As the precursor of the perovskite compound,there can be cited, for example, a mixture of methylammonium halide andlead halide or tin halide. The active layer is formed by applying thesolution in which the perovskite compound or its precursor is dissolvedin the solvent, followed by heating and drying. Alternatively, theactive layer can also be formed by applying and drying a solution oflead halide or tin halide as the precursor and thereafter applying asolution of methylammonium halide, followed by heating and drying.

A kind of the solvent is not limited in particular as long as theperovskite compound or its precursor can be dissolved in the solventuniformly. The solvent is selected from, for example, low alcohols suchas methanol, ethanol, propanol, ethylene glycol, and methoxyethanol,ketones such as acetone, methyl ethyl ketone, cyclopentanone, andcyclohexanone, esters such as ethyl acetate, butyl acetate, and methyllactate, ethers such as ethyl ether, tetrahydrofuran, and dioxane, andamides such as dimethylformamide and dimethylacetamide.

A thickness of the active layer is not limited in particular, but ispreferably not less than 10 nm nor more than 1000 nm, and morepreferably not less than 50 nm nor more than 600 nm. When the thicknessof the active layer is 10 nm or more, uniformity of the active layer ismaintained and a short circuit is hard to occur. When the thickness ofthe active layer is 1000 nm or less, an internal resistance can be madesmall, and further since a distance between the electrodes becomessmall, it is possible to diffuse charges in a good condition.

In the organic/inorganic hybrid solar cell of the embodiment, the holeextraction layer (buffer layer) formed of the p-type semiconductormaterial containing the polymer of the embodiment described above isprovided between the active layer and the anode electrode. The holeextraction layer is formed by applying a solution in which the polymeris dissolved in a solvent, for instance. A thickness of the holeextraction layer is not limited in particular, but normally is not lessthan 1 nm nor more than 100 nm. The thickness of the hole extractionlayer is preferably not less 2 nm nor more than 50 nm. If the thicknessof the hole extraction layer is too small, uniformity becomesinsufficient and a short circuit tends to occur. If the thickness of thehole extraction layer is too large, a resistance value increases and ittends to be difficult to extract a hole.

The organic/inorganic hybrid solar cell of the embodiment, similarly tothe aforesaid organic thin film solar cell, may include the electronextraction layer (buffer layer) provided between the active layer andthe cathode electrode. A forming material and a forming method of theelectron extraction layer are as previously described. Further, formingmaterials of the anode electrode and the cathode electrode are also aspreviously described. Other structure of the organic/inorganic hybridsolar cell is also the same as that of the previously described organicthin film solar cell.

EXAMPLES

Next, examples and their evaluation results will be described.

[Synthesis Example of Acceptor Unit Monomer]

A monomer used for synthesizing a polymer was synthesized. A syntheticpathway of the monomer is shown below.

(Synthesis of Compound MA2)

A 18.63 g (0.100 mol) compound MA1 was weighed and fed into a four-neckflask, a thermometer, an argon conduit, and a dropping funnel wereattached thereto, a rotor was put therein, and nitrogen was supplied toproduce a nitrogen atmosphere, and thereafter 400 mL anhydroustetrahydrofuran (THF) was added. A 138 mL hexane solution of 1.6 Mn-butyllithium was put into the dropping funnel. After the flask wascooled to −78° C. by dry ice/acetone bathing, the solution was graduallydropped from the dropping funnel. After the dropping, a reaction wascaused for two hours at this temperature. While this temperature waskept, a solution in which 21.36 g N-bromosuccinimide was dissolved in100 mL anhydrous THF was gradually added from the dropping funnel. Theywere made to react for six hours. After the temperature was returned toa room temperature, a reaction mixture was poured into water and wasmade acid by hydrochloric acid, and thereafter extraction with ether wascarried out. An organic layer was dried by a magnesium sulfateanhydride, a solvent was removed under a reduced pressure, and a 14.32 g(yield 54%) dull yellowish white solid body of a compound MA2 wasobtained.

(Synthesis of Compound MA3)

Under an argon atmosphere, a rotor for a magnetic stirrer was put in apressure resistant pipe (30 mL) for a microwave synthesizing apparatus,2.652 g (0.010 mol) of the compound MA2 was weighed and fed thereto, and0.45 g sodium hydroxide and 4.5 mL water were added. Further, a 4.32 g25% NaSO₃ aqueous solution and a 1.5 mL 30% NaOH aqueous solution wereadded, and after they were stirred, 0.081 g copper chloride (I) wasadded, and the pressure resistant pipe was covered by a specialized cap.The aforesaid pressure resistant pipe was set to the microwavesynthesizing apparatus, and was heated at 140° C. for 9 hours. Aftercooling to a room temperature, a deposit was removed by filtration by aglass filter, 4 mL concentrated hydrochloric acid was added to afiltrate to make the filtrate acid, and extraction with ethyl acetatewas carried out. Drying by a magnesium sulfate anhydride was carriedout, the solvent was removed under a reduced pressure, and a 1.194 g(yield 45.0%) brown solid body of a compound MA3 was obtained.

(Synthesis of Compound MA5a)

A rotor was put into a three-neck flask provided with a thermometer, areflux tube with an argon conduit, and a dropping funnel, and 1.061 g(4.00 mmol) of the compound MA3 and 1.668 g phosphorus pentachloridewere added thereto. After an argon atmosphere was produced, 10 mLphosphorus oxychloride was gradually dropped from the dropping funnelalong with stirring by a magnetic stirrer. After the dropping wasfinished, they were made to react for 3 hours at a reflux temperature.After the phosphorus oxychloride was removed under a reduced pressure, aresidue was dissolved in anhydrous trichloromethane (TCM), and a depositwas removed by filtration by a glass filter. A filtrate was condensedunder a reduced pressure and a khaki solid body of a compound MA4 wasobtained. Then, a next reaction was carried out without refinement.

The solid body of the compound MA4 and a 10 mL toluene anhydride wereadded to a flask provided with a reflux cooling tube with an argonconduit and a dropping funnel, and a solution in which 0.810 g (8.00mmol) triethylamine and 0.708 g (4.00 mmol) n-octylamine were dissolvedin a 10 mL toluene anhydride was added by the dropping funnel under aroom temperature. After the dropping, they were made to react for 8hours at a heat reflux temperature. After cooling, toluene was added,and after washing by ion exchanged water, dilute hydrochloric acid, andion exchanged water in the order mentioned, drying was carried out by amagnesium sulfate anhydride, condensation was carried out under areduced pressure, and a bister solid body was obtained. This was refinedby column chromatography (silica gel, developing solvent: toluene), anda 0.892 g (yield 62.0%) compound MA5a was obtained.

(Synthesis of Compound MA5b)

A compound MA5b was synthesized by the same method as that forsynthesizing the compound MA5a except that 2-ethylhexylamine was usedinstead of n-octylamine used for synthesizing the compound MA5a. A solidbody of the compound MA5b was obtained with a 78% yield.

(Synthesis of Compound MA5c)

A compound MA5c was synthesized by the same method as that forsynthesizing the compound MA5a except that 4-(n-octyl)aniline was usedinstead of n-octylamine used for synthesizing the compound MA5a. A solidbody of the compound MA5c was obtained with a 72.4% yield.

(Synthesis of Compound MA5d)

A compound MA5d was synthesized by the same method as that forsynthesizing the compound MA5a except that 2-bromopropylaminehydrochloride was used instead of n-octylamine used for synthesizing thecompound MA5a. A solid body of the compound MA5d was obtained with a 70%yield.

(Synthesis of Compound MA6a)

After a four-neck flask provided with a thermometer, a reflux tube withan argon conduit, and a dropping funnel was set to an argon atmosphere,0.719 g (2.00 mmol) of the compound MA5a was weighed and fed thereto,and 5 mL anhydrous TCM was added. A solution in which 0.480 g (72 wt %,2.00 mmol) m-chloroperbenzoic acid was dissolved in 10 mL anhydrous TCMwas put into the dropping funnel. After the flask was cooled to −40° C.,the solution was dropped from the dropping funnel. After the dropping,the temperature was returned to a room temperature and they were made toreact for 3 hours. A 20 mL acetic anhydride was added to a reactionproduct obtained after a solvent was removed under a reduced pressure,and they were heated to react for 20 minutes at a solvent refluxtemperature. After the solvent was removed under a reduced pressure,refining was carried out by column chromatography (silica gel,developing solvent; hexane:toluene=1:1), and a 0.608 g (yield 85.0%)solid body of a compound MA6a was obtained.

(Synthesis of Compound MA6b)

A compound MA6b was synthesized by the same method as that forsynthesizing the compound MA6a except that the compound MA5b was usedinstead of the compound MA5a used for synthesizing the compound MA6a. Asolid body of the compound MA6b was obtained with a 78.3% yield.

(Synthesis of Compound MA6c)

A compound MA6c was synthesized by the same method as that forsynthesizing the compound MA6a except that the compound MA5c was usedinstead of the compound MA5a used for synthesizing the compound MA6a. Asolid body of the compound MA6c was obtained with a 82.6% yield.

(Synthesis of Compound MA6d)

A compound MA6d was synthesized by the same method as that forsynthesizing the compound MA6a except that the compound MA5d was usedinstead of the compound MA5a used for synthesizing the compound MA6a. Asolid body of the compound MA6d was obtained with a 83.7% yield.

(Synthesis of Dibromo-substituted Monomer AMa)

0.536 g (1.50 mmol) of the compound MA6a and a 5 mL DMF anhydride wereadded to a three-neck flask provided with a reflux tube, a droppingfunnel, and a rotor. A solution in which 0.667 g (3.75 mmol)N-bromosuccinimide was dissolved in a 20 mL DMF anhydride was put intothe dropping funnel. The solution was dropped from the dropping funnelunder a room temperature. After the dropping, they were made to reactfor one day at the room temperature. A sodium thiosulfate solution wasadded, and after processing was carried out for 30 minutes, extractionwas performed by chloroform, and washing was performed twice by water,and washing was performed once by a NaCl aqueous solution. An organiclayer was dried by a magnesium anhydride. Under a reduced pressure, asolvent was concentrated, a residue was refined by column chromatography(silica gel, developing solvent; hexane:toluene=2:1), and a 0.607 g(yield 78.5%) solid body of a monomer AMa was obtained

(Synthesis of Dibromo-Substituted Monomer AMb)

A monomer AMb was synthesized by the same method as that forsynthesizing the monomer AMa except that the compound MA6b was usedinstead of the compound MA6a used for synthesizing the monomer AMa. Asolid body of the monomer AMb was obtained with a 88.3% yield.

(Synthesis of Dibromo-Substituted Monomer AMc)

A monomer AMc was synthesized by the same method as that forsynthesizing the monomer AMa except that the compound MA5c was usedinstead of the compound MA6a used for synthesizing the monomer AMa. Asolid body of the monomer AMc was obtained with a 91.1% yield.

(Synthesis of Dibromo-Substituted Monomer AMd)

A monomer AMd was synthesized by the same method as that forsynthesizing the monomer AMa except that the compound MA5c was usedinstead of the compound MA6a used for synthesizing the monomer AMa. Asolid body of the monomer AMd was obtained with a 87.5% yield.

[Example of Synthesis of Donor Unit Monomer]

A monomer MD1 shown below was synthesized according to the methoddescribed in Jivanhui Hou et al., Macromolecules, 2008, Vol. 41, 6021. Amonomer MD2 shown below was synthesized according to the methoddescribed in Yongye Liang et al., J. Am. Chem. Soc. 2009, Vol. 131, No.22, 7792-7799.

Example 1

A polymer P1 shown below was synthesized.

Under nitrogen, 0.452 g (0.500 mmol) of the monomer MD1, 0.258 g (0.500mmol) of the monomer AMa, and 0.024 gtetrakis(triphenylphosphine)palladium (catalyst) were weighed and fedinto a three-neck flask provided with a three-way cock, and while argonwas made to flow into the three-neck flask through the three-way cock, areflux tube with an argon conduit was attached to the three-neck flask.Subsequently, in order to prevent deactivation of the catalyst due tointerfusion of air, a dropping funnel was provided in a manner that theair does not enter. The argon conduit was connected to a vacuum line, sothat switching between argon and vacuum was available. The three-waycock was closed, the inside of the flask was vacuumized, and argon wasintroduced again. The above operation was repeated three times.

The three-way cock (into which the argon was made to flow from one side)attached to the three-neck flask was opened, and an 8 mL tolueneanhydride which has been degassed and a 2 mL DMF anhydride were added bya syringe and dissolved. By heating the three-neck flask in an oil bath,they were made to react at a reflux temperature for 12 hours, andthereafter the three-neck flask was cooled to a room temperature. Undernitrogen, 0.062 g trimethylphenyltin was weighed as an end capping agentand dissolved in a 4 mL toluene anhydride having been degassed, and theresultant was added into the three-neck flask by a syringe similarly tothe above, and heat refluxing was carried out for 2 hours. After coolingdown to the room temperature, under nitrogen, 0.058 g bromobenzene wasweighed as another end capping agent and dissolved into a 4 mL tolueneanhydride having been degassed, and the resultant was added into theflask by a syringe similarly to the above, and heat refluxing wascarried out for 2 hours.

After cooling down to the room temperature, the above reaction solutionwas dropped into 500 mL methanol while being stirred, to precipitate apolymer. The precipitate, after being filtered by a glass filter, wasdissolved into chloroform, and then the catalyst was removed through acelite column. The solvent was condensed by an evaporator, and methanolwas further added, and after they were well stirred, filtration by usinga glass filter was carried out to obtain a solid body. This solid bodywas vacuum-dried at 80° C. for 4 hours, and a polymer being a glossyblack solid body was quantitatively obtained. By Soxhlet extraction,this was refined with ethyl acetate, hexane, and toluene in the ordermentioned. Thereafter, a benzene extract component was used. A yield ofthe benzene extract component was 87.2%.

The obtained solid body was evaluated by using an NMR device (JNM-GSX270(brand name), produced by JEOL Ltd.). An obtained result was “1H-NMR(270 MHz, CDCI 3) ∂: 8.1 to 6.7 (Broad), 3.4 to 2.75 (Broad), 1.87 to0.6 (m)”. A peak of an aromatic proton of a benzothiophene ring and athiophene ring of a side chain was observed at 6.7 to 8.1 ppm, a peakcorresponding to CH₂ bonded to N and CH₂ bonded to a thiophene ring of aside chain was observed at 2.75 to 3.4 ppm, and a peak corresponding toan alkyl group was observed at 0.6 to 1.87 ppm, and it was confirmedthat the obtained solid body was an intended polymer. An evaluation bygel permeation chromatography was also carried out.

When a weight-average molecular weight of polystyrene conversion wasmeasured by using a GPC device (HPCL: CBM20 (brand name) produced bySHIMADZU CORPORATION, column: K-504 produced by Shodex, solvent:chloroform), and it was 84600 (Mw/Mn=2.5). An UV-vis absorption spectrum(by using A2000 (brand name) produced by SHIMADZU CORPORATION, and achloroform solution) was measured, and an absorption peak (λmax) was 678nm.

Example 2

A polymer P2 shown below was synthesized.

A polymer being a glossy black solid body was obtained by a synthesisunder the same condition as that in Example 1 except that the monomerMD2 was used instead of the monomer MD1 used in Example 1. By Soxhletextraction, it was refined with ethyl acetate, hexane, toluene, andchlorobenzene in the order mentioned. Thereafter, a benzene extractcomponent was used. A yield of the benzene extract component was 93.7%.

When the obtained solid body was evaluated by using an NMR device, anobtained result was “1H-NMR (270 MHz, CDCl3) ∂: 8.0 to 7.2 (Broad), 4.3to 3.2 (Broad), 2.1 to 0.6 (m)”. A peak of an aromatic proton of abenzothiophene ring was observed at 7.2 to 8.0 ppm, a peak correspondingto CH₂ bonded to oxygen of a side chain and CH₂ bonded to N was observedat 3.2 to 4.3 ppm, and a peak corresponding to an alkyl group wasobserved at 0.6 to 2.1 ppm, and it was confirmed that the obtained solidbody was an intended polymer. When a weight-average molecular weight andan UV-vis absorption spectrum were further measured by the same methodsas those described above, the weight-average molecular weight ofplystyrene conversion was 78600 (Mw/Mn=2.2) and an absorption peak(λmax) was 670 nm.

Example 3

A polymer P3 shown below was synthesized.

A polymer being a glossy black solid body was obtained by a synthesisunder the same condition as that in Example 1 except that the monomerAMb was used instead of the monomer AMa used in Example 1. By Soxhletextraction, it was refined with ethyl acetate, hexane, toluene, andchlorobenzene in the order mentioned. Thereafter, a benzene extractcomponent was used. A yield of the benzene extract component was 93.7%.

When the obtained solid body was evaluated by using an NMR device, anobtained result was “1H-NMR (270 MHz, CDCl3) ∂: 8.2 to 6.7 (Broad), 3.8to 2.5 (Broad), 2.1 to 0.6 (m)”. A peak of an aromatic proton of abenzothiophene ring and a thiophene ring of a side chain was observed at6.7 to 8.2 ppm, a peak corresponding to CH₂ bonded to a thiophene ringof a side chain and CH₂ bonded to N was observed at 2.5 to 3.8 ppm, anda peak corresponding to an alkyl group was observed at 0.6 to 2.1 ppm,and it was confirmed that the obtained solid body was an intendedpolymer. When a weight-average molecular weight and an UV-vis absorptionspectrum were further measured by the same methods as those describedabove, the weight-average molecular weight of plystyrene conversion was6300 (Mw/Mn=2.3) and an absorption peak (λmax) was 664 nm.

Example 4

A polymer P4 shown below was synthesized.

A polymer being a glossy black solid body was obtained by a synthesisunder the same condition as that in Example 3 except that the monomerMD2 was used instead of the monomer MD1 used in Example 3. By Soxhletextraction, it was refined with ethyl acetate, hexane, toluene, andchlorobenzene in sequence. Thereafter, a benzene extract component wasused. A yield of the benzene extract component was 93.7%.

When the obtained solid body was evaluated by using an NMR device, anobtained result was “1H-NMR (270 MHz, CDCl3) ∂: 7.9 to 7.1 (Broad), 4.3to 3.2 (Broad), 2.1 to 0.6 (m)”. A peak of an aromatic proton of abenzothiophene ring and a thiophene of a side chain was observed at 7.1to 7.9 ppm, a peak corresponding to CH₂ bonded to oxygen of a side chainand CH₂ bonded to N was observed at 3.2 to 4.3 ppm, and a peakcorresponding to an alkyl group was observed at 0.6 to 2.1 ppm, and itwas confirmed that the obtained solid body was an intended polymer. Whena weight-average molecular weight and an UV-vis absorption spectrum werefurther measured by the same methods as those described above, theweight-average molecular weight of plystyrene conversion was 78600(Mw/Mn=2.2) and an absorption peak (λmax) was 660 nm.

Example 5

A polymer P5 shown below was synthesized.

A polymer being a glossy black solid body was obtained by a synthesisunder the same condition as that in Example 1 except that the monomerAMc was used instead of the monomer AMa in Example 1. By Soxhletextraction, it was refined with ethyl acetate, hexane, toluene, andchlorobenzene in the order mentioned. Thereafter, a benzene extractcomponent was used. A yield of the benzene extract component was 79%.

When the obtained solid body was evaluated by using an NMR device, anobtained result was “1H-NMR (270 MHz, CDCl3) ∂: 8.1 to 6.7 (Broad), 3.9to 2.6 (Broad), 2.4 to 0.6 (m)”. A peak of an aromatic proton of abenzene ring, a benzothiophene ring, and a thiophene ring of a sidechain was observed at 6.7 to 8.1 ppm, a peak corresponding to CH₂ bondedto a thiophene ring of a side chain and CH₂ bonded to N was observed at2.6 to 3.9 ppm, and a peak corresponding to an alkyl group was observedat 0.6 to 2.4 ppm, and it was confirmed that the obtained polymer was anintended polymer. When a weight-average molecular weight and an UV-visabsorption spectrum were further measured by the same methods as thosedescribed above, the weight-average molecular weight of plystyreneconversion was 88500 (Mw/Mn=2.7) and an absorption peak (λmax) was 685nm.

Example 6

A polymer P6 shown below was synthesized.

A polymer being a glossy black solid body was obtained by a synthesisunder the same condition as that in Example 5 except that the monomerMD2 was used instead of the monomer MD1 used in Example 5. By Soxhletextraction, it was refined with ethyl acetate, hexane, toluene, andchlorobenzene in the order mentioned. Thereafter, a benzene extractcomponent was used. A yield of the benzene extract component was 82%.

When the obtained solid body was evaluated by using an NMR device, anobtained result was “1H-NMR (270 MHz, CDCl3) ∂: 8.2 to 6.5 (Broad), 4.4to 3.7 (Broad), 2.6 to 0.6 (m)”. A peak of an aromatic proton of abenzothiophene ring and a benzene ring of a side chain was observed at6.5 to 8.2 ppm, a peak corresponding to CH₂ bonded to oxygen wasobserved at 3.7 to 4.4 ppm, and a peak corresponding to an alkyl groupwas observed at 0.6 to 2.6 ppm, and it was confirmed that the obtainedsolid body was an intended polymer. When a weight-average molecularweight and an UV-vis absorption spectrum were further measured by thesame methods as those described above, the weight-average molecularweight of plystyrene conversion was 71500 (Mw/Mn=2.4) and an absorptionpeak (λmax) was 675 nm.

Example 7

A polymer P7 shown below was synthesized.

A polymer being a glossy black solid body was obtained by a synthesisunder the same condition as that in Example 1 except that the monomerAMd was used instead of the monomer AMa used in Example 1. By Soxhletextraction, it was refined with ethyl acetate, hexane, toluene, andchlorobenzene in the order mentioned. Thereafter, a benzene extractcomponent was used. A yield of the benzene extract component was 79%.

When the obtained solid body was evaluated by using an NMR device, anobtained result was “1H-NMR (270 MHz, CDCl3) ∂: 8.1 to 6.7 (Broad), 3.9to 2.6 (Broad), 2.4 to 0.6 (m)”. A peak of an aromatic proton of abenzene ring, a benzothiophene ring, and a benzene ring of a side chainwas observed at 6.7 to 8.1 ppm, a peak corresponding to CH₂ bonded to N,CH₂ bonded to Br, and CH₂ bonded to a thiophene ring of a side chain wasobserved at 2.6 to 3.9 ppm, and a peak corresponding to an alkyl groupwas observed at 0.6 to 2.4 ppm, and it was confirmed that the obtainedsolid body was an intended polymer. When a weight-average molecularweight and an UV-vis absorption spectrum were further measured by thesame methods as those described above, the weight-average molecularweight of plystyrene conversion was 66700 (Mw/Mn=2.8) and an absorptionpeak (λmax) was 655 nm.

Example 8

A polymer P8 shown below was synthesized.

A polymer being a glossy black solid body was obtained by a synthesisunder the same condition as that in Example 1 except that a mixture ofthe monomer AMa and the monomer AMc (AMa:AMc=4:1 (mole ratio)) was usedinstead of the monomer AMa used in Example 1. By Soxhlet extraction, itwas refined with ethyl acetate, hexane, toluene, and chlorobenzene inthe order mentioned. Thereafter, a benzene extract component was used. Ayield of the benzene extract component was 75%.

When the obtained solid body was evaluated by using an NMR device, anobtained result was “1H-NMR (270 MHz, CDCl3) ∂: 8.0 to 6.5 (Broad), 4.0to 2.6 (Broad), 2.3 to 0.6 (m)”. A peak of an aromatic proton of abenzothiophene ring and a thiophene ring of a side chain was observed at6.5 to 8.0 ppm, a peak corresponding to CH₂ bonded to Br, CH₂ bonded toBr, and CH₂ bonded to a thiophene ring of a side chain was observed at2.6 to 4.0 ppm, and a peak corresponding to an alkyl group was observedat 0.6 to 2.3 ppm, and it was confirmed that the obtained solid body wasan intended polymer. When a weight-average molecular weight and anUV-vis absorption spectrum were further measured by the same methods asthose described above, the weight-average molecular weight of plystyreneconversion was 59300 (Mw/Mn=3.2) and an absorption peak (λmax) was 649nm.

Fabrication of Organic Thin Film Solar Cell Elements Examples 9 to 16,Comparative Example 1

The polymers (P1 to P8) of the examples 1 to 8 and, as a comparativeexample 1, poly(3-hexylthiophene-2,5-diyl) (P3HT), which are p-typesemiconductor materials, were mixed with PC70BM being an n-typesemiconductor material so that a mass ratio with PC70BM became 1:2.Next, the mixtures were dissolved in chlorobenzene in a nitrogenatmosphere so that the concentration of each of the mixtures became 2.0mass %. 1.8-diiodooctane was added so that its ratio became 3 mass % ofthe whole solution, and the resultants were mixed by stirring at a 120°C. temperature for one hour by using a hot stirrer. The solutions havingbenn mixed by stirring were cooled to a room temperature, and thereafterfiltered by a 0.20 μm polytetrafluoroethylene (PTFE) filter, so thatactive layer coating solutions using the respective polymers wereobtained.

After glass substrates on each of which a transparent conduction film ofan indium tin oxide (ITO) was patterned were washed by ultrasoniccleaning with a surface active agent, water washing with ultrapurewater, and ultrasonic cleaning with ultrapure water in the ordermentioned, the glass substrates were dried by nitrogen blowing, and thendried by heating at 120° C. for 5 minutes in the atmosphere. Lastly,ultraviolet ozone cleaning was performed to the substrates. On each ofthe substrates, as an electron extraction layer, a diethoxyethanesolution (2%, manufactured by SHOWA DENKO K.K.) of diethyl zinc being aprecursor of a zinc oxide was applied by spin coating in a nitrogenatmosphere, and the coated substrates were heated on a hot plate at 150°C. for 10 minutes in the atmosphere. A film thickness of the electronextraction layers was about 20 nm.

On the substrates on each which the hole extraction layer was formed,the active layer coating solutions of the polymers were applied by spincoating at a speed of 600 rpm under a nitrogen atmosphere, and therebyactive layers with an about 90 nm thickness were formed. Thereafter, avanadium oxide film with a 2 nm average film thickness as a holeextraction layer and silver with a 100 nm thickness as an electrodelayer were sequentially formed by a resistance heating vacuum depositionmethod. 1 cm square solar cell elements were fabricated as describedabove.

Examples 17 to 18

In the same manner as in the examples 9 to 16, active layer coatingsolutions of the polymer [P7] of the example 7 and the polymer [P8] ofthe example 8 were applied on substrates on each of which an electronextraction layer was formed, by spin coating at a speed of 600 rpm undera nitrogen atmosphere, whereby active layers with an about 90 nmthickness were formed. Next, the active layers were subjected tophotocross linking by irradiation of UV light (254 nm, 1.9 mW/cm²) for30 minutes under an argon atmosphere. Thereafter, hole extraction layersand electrode layers were formed in the same manner as in the examples 9to 16, whereby 1 cm square solar cell elements were fabricated.

[Evaluation of Organic Thin Film Solar Cell Elements]

1 cm square metal masks were attached to the fabricated solar cellelements and a current-voltage characteristic between an ITO electrodeand an Ag electrode was measured by using SPECTR solar simulator IVP0605(brand name) with an air mass (AM) of 1.5 G and an irradiance of 100mW/cm² produced by Asahi Spectra Co., Ltd. as an irradiation lightsource. Table 1 shows open circuit voltage (Voc), short-circuit currentdensity (Jsc), filter factor (FF), conversion efficiency as measurementresults.

In order to evaluate durability of the solar cell elements whosepolymers were photocross-linked and the solar cell elements whosepolymers were not photocross-linked, a light deterioration rate and aheat deterioration rate were measured. The light deterioration rate wasevaluated by conducting a light resistance test in conformity with C8938of the JIS Standard. An irradiation light source with a 1.5 G air mass(AM) and a 100 mW/cm² irradiance was used and a black panel temperaturewas adjusted to 63° C., and irradiation was performed continuously for70 hours. After the light irradiation, a current-voltage characteristicwas similarly measured, and the light deterioration rate was found. Theheat deterioration rate was found by similarly measuring acurrent-voltage characteristic after 30-minute heating at 100° C. in anitrogen atmosphere. Results of these are shown in Table 1.

TABLE 1 Evaluation result of characteristic of organic thin film solarcell Open circuit Short-circuit Power Deterioration rate voltage currentdensity generation Light Heat (Voc) (Jsc) Fill factor efficiencydeterioration deterioration Polymer [V] [mA/cm²] (FF) [%] [%] [%]Example 9 Example 1 [P1] 0.94 13.5 0.61 7.74 — — Example 10 Example 2[P2] 0.91 12.3 0.60 6.72 — — Example 11 Example 3 [P3] 0.96 12.8 0.597.25 — — Example 12 Example 4 [P4] 0.93 11.8 0.58 6.36 — — Example 13Example 5 [P5] 0.94 12.5 0.58 6.82 — — Example 14 Example 6 [P6] 0.9212.1 0.59 6.57 — — Example 15 Example 7 [P7] 0.96 11.8 0.57 6.46 13 28Example 16 Example 8 [P8] 0.96 12.3 0.58 6.85 11 27 Example 17 Example 7[P7] + 0.95 11.0 0.56 5.85 3 9 photocross linking Example 18 Example 8[P8] + 0.95 11.2 0.56 5.96 3 8 photocross linking Comparative P3HT 0.568.5 0.60 2.86 — — Example 1

As is obvious from Table 1, it is understood that the solar cellelements using the polymers of the examples are higher in open circuitvoltage (Voc) than the comparative example by about 0.3 V to about 0.4V. Therefore, by using the polymers of the examples, it becomes possibleto provide a high-performance organic thin film solar cell. Further, bysubjecting the polymer to the cross linking, it is possible to improvelight resistance and heat resistance.

Fabrication of Organic/Inorganic Hybrid Solar Cell Element Examples 19to 25

Lead iodide (PbI₂) and methylammonium iodide (CH₃NH₄I) were mixed at a1:1 mole ratio, and this mixture was dissolved in dimethylformamide in anitrogen atmosphere so that its concentration became 40 mass %. Thissolution was mixed by stirring at a 120° C. temperature for one hour byusing a hot stirrer. After the solution having been mixed by stirringwas cooled to a room temperature, it was filtered by a 0.45polytetrafluoroethylene (PTFE) filter, so that an active layer coatingsolution was obtained.

The polymers (P1 to P7) of the examples 1 to 7 being p-typesemiconductor materials were dissolved in chlorobenzene in a nitrogenatmosphere so that their concentration became 1.0 mass %. Thesesolutions were mixed by stirring at a 120° temperature for one hour byusing a hot stirrer. After the solutions having been mixed by stirringwere cooled to a room temperature, they were filtered by a 0.20 μm PTFEfilter, so that hole extraction layer coating solutions using therespective polymers were obtained.

After glass substrates on each of which a transparent conduction film ofa fluorine-doped tin oxide (FTO) was patterned were washed by ultrasoniccleaning with a surface active agent, water washing with ultrapurewater, and ultrasonic cleaning with ultrapure water in the ordermentioned, the glass substrates were dried by nitrogen blowing, and thendried by heating at 120° C. for 5 minutes in the atmosphere. Lastly,ultraviolet ozone cleaning was performed to the substrates. On thesubstrates, an ethanol solution of titanium diisopropoxidebis(acetylacetone) was applied by spin coating, and they were cooledafter being heated at 450° C. for 30 minutes. The substrates wereimmersed in a titanium chloride (TiCl₄) aqueous solution at 70° C. for30 minutes. After the substrates taken out from the aqueous solutionwere washed and dried, they were heated at 500° C. for 20 minutes in theair, so that electron extraction layers having an about 20 nm thicknesswere formed.

The substrates on each of which the electron extraction layer was formedwere spin-coated with the active layer coating solution of a perovskitecompound at 600 rpm in a nitrogen atmosphere and were dried at 60° C.for 30 minutes, so that active layers having an about 300 nm thicknesswere formed. The hole extraction layer coating solutions of the polymerswere applied on the respective active layers by spin coating at 2000 rpmspeed for 60 seconds, so that hole extraction layers were formed.Thereafter, films of gold with a 100 nm thickness as electrode layerswere formed by a resistance heating vacuum deposition method. In thismanner, 1 cm square organic/inorganic hybrid solar cell elements werefabricated.

Comparative Example 2

An organic/inorganic hybrid solar cell element was fabricated in thesame manner as in the example 19 except thatpoly(3-hexylthiophene-2,5-diyl) (P3HT) was used as a forming material ofa hole extraction layer.

Comparative Example 3

An organic/inorganic hybrid solar cell element was fabricated in thesame manner as in the example 19 except that a hole extraction layer wasformed as follows. 180 mg2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-bifluorene(spiro-OMeTAD)was dissolved in 1 mL dichlorobenzene. In this solution, 37.5 μLsolution in which 170 mg bis(trifluoromethanesulfonyl)imidelithium(Li-TFSI) was dissolved in 1 mL acetonitrile was added, and further 17.5μL 4-t-butylpyridine was added, whereby a hole extraction layer coatingsolution was prepared. This hole extraction layer coating solution wasapplied by spin coating at a 3000 rpm speed for 30 seconds, whereby ahole extraction layer was formed.

[Evaluation of Organic/Inorganic Hybrid Solar Cell Elements]

Metal masks of 1 cm square were attached to the organic/inorganic hybridsolar cell elements and a current-voltage characteristic between an FTOelectrode and an Au electrode was measured by using SPECTR solarsimulator IVP0605 (brand name) with an air mass (AM) of 1.5 G and anirradiance of 100 mW/cm² produced by Asahi Spectra Co., Ltd. as anirradiation light source. Table 2 shows open circuit voltage (Voc),short-circuit current density (Jsc), filter factor (FF), conversionefficiency as measurement results. Further, after the organic/inorganichybrid solar cell elements were sealed with glass, they were heated on ahot plate at 90° C. for 15 minutes in a nitrogen atmosphere, andthereafter they were cooled to a room temperature. After a heating test,the same characteristics were measured and a deterioration rate wasfound. Table 2 shows the deterioration rate of the characteristicsbefore and after the heating.

TABLE 2 Evaluation result of characteristic of organic thin film solarcell Short-circuit Open circuit current Power voltage density Fillgeneration Deterioration (Voc) (Jsc) factor efficiency rate Polymer [V][mA/cm²] (FF) [%] [%] Example 19 Example 1 [P1] 0.81 15.2 0.63 7.76 5Example 20 Example 2 [P2] 0.78 14.9 0.62 7.21 4 Example 21 Example 3[P3] 0.79 14.9 0.60 7.06 5 Example 22 Example 4 [P4] 0.83 13.8 0.59 6.766 Example 23 Example 5 [P5] 0.81 14.5 0.58 6.81 3 Example 24 Example 6[P6] 0.79 13.8 0.59 6.43 3 Example 25 Example 7 [P7] 0.83 12.3 0.58 5.924 Comparative P3HT 0.50 10.5 0.65 3.41 4 Example 2 ComparativeSpiro-OMeTAD + 0.93 18.3 0.64 9.72 75 Example 3 Li-TFSI

As is obvious from Table 2, it is understood that the organic/inorganichybrid solar cell elements using the polymers of the examples aresuperior in the characteristics such as the open circuit voltage and thepower generation efficiency as compared with the comparative example 1,and are superior in heat resistance as compared with the comparativeexample 2. Therefore, by using the polymers of the examples, it becomespossible to provide a high-performance organic/inorganic hybrid solarcell having a long life.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods described herein maybe embodied in a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods described hereinmay be made without departing from the spirit of the inventions. Theaccompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of theinventions.

What is claimed is:
 1. A polymer comprising a repeating unit containinga bivalent group represented by the following formula (1),

wherein R is a monovalent group selected from hydrogen, halogen, a cyanogroup, a nitro group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted alkanoyl group, a substituted orunsubstituted aryl group, or a substituted or unsubstituted heteroarylgroup, X is an atom selected from oxygen, sulfur, or selenium, and Y andZ are each independently a bivalent group selected from a carbonylgroup, a sulfinyl group, or a sulfonyl group, with a case where Y and Zare both the carbonyl groups being excluded.
 2. The polymer of claim 1,comprising a repeating unit represented by the following formula (2),

wherein R is a monovalent group selected from hydrogen, halogen, a cyanogroup, a nitro group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted alkanoyl group, a substituted orunsubstituted aryl group, or a substituted or unsubstituted heteroarylgroup, X is an atom selected from oxygen, sulfur, or selenium, and Y andZ are each independently a bivalent group selected from a carbonylgroup, a sulfinyl group, or a sulfonyl group, with a case where Y and Zare both the carbonyl groups being excluded.
 3. The polymer of claim 2,further comprising a monovalent group including a cross-linking group asan end group of the polymer.
 4. The polymer of claim 1, comprising arepeating unit represented by the following formula (3),

wherein R is a monovalent group selected from hydrogen, halogen, a cyanogroup, a nitro group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted alkanoyl group, a substituted orunsubstituted aryl group, or a substituted or unsubstituted heteroarylgroup, X is an atom selected from oxygen, sulfur, or selenium, Y and Zare each independently a bivalent group selected from a carbonyl group,a sulfinyl group, or a sulfonyl group, with a case where Y and Z areboth the carbonyl groups being excluded, and Ar is a substituted orunsubstituted bivalent conjugated group.
 5. The polymer of claim 4,further comprising a monovalent group including a cross-linking group asan end group of the polymer.
 6. The polymer of claim 1, comprising arepeating unit represented by the following formula (4),

wherein R is a monovalent group selected from hydrogen, halogen, a cyanogroup, a nitro group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted alkanoyl group, a substituted orunsubstituted aryl group, or a substituted or unsubstituted heteroarylgroup, X and X′ are each independently an atom selected from a groupconsisting of oxygen, sulfur, or selenium, Y, Y′, Z, and Z′ are eachindependently a bivalent group selected from a carbonyl group, asulfinyl group, or a sulfonyl group, with a case where Y and Z are boththe carbonyl groups being excluded and with a case where Y′ and Z′ areboth the carbonyl groups being excluded, and R′ is a monovalent grouphaving a cross-linking group.
 7. The polymer of claim 1, comprising arepeating unit represented by the following formula (5),

wherein at least one selected from R′ or Ar′ is a substituent having across-linking group, R and R′ which does not have the cross-linkinggroup are each independently a monovalent group selected from hydrogen,halogen, a cyano group, a nitro group, a substituted or unsubstitutedalkyl group, a substituted or unsubstituted alkanoyl group, asubstituted or unsubstituted aryl group, or a substituted orunsubstituted heteroaryl group, X and X′ are each independently an atomselected from oxygen, sulfur, or selenium, Y, Y′, Z, and Z′ are eachindependently a bivalent group selected from a carbonyl group, asulfinyl group, or a sulfonyl group, with a case where Y and Z are boththe carbonyl groups being excluded and with a case where Y′ and Z′ areboth the carbonyl groups being excluded, and Ar and Ar′ which does nothave the cross-linking group are each a substituted or unsubstitutedbivalent conjugated group.
 8. The polymer of claim 1, wherein aweight-average molecular weight of the polymer is not less than 3000 normore than
 1000000. 9. A solar cell comprising the polymer of claim 1.10. A solar cell comprising: a first electrode, a second electrode, anda photoelectric conversion layer disposed between the first and secondelectrodes and containing an organic material, wherein the organicmaterial contains the polymer of claim
 1. 11. The solar cell of claim10, wherein the photoelectric conversion layer has an active layercontaining the polymer.
 12. The solar cell of claim 10, wherein thephotoelectric conversion layer has a buffer layer containing thepolymer.